1. Field of the Invention
The present invention relates to a perforating apparatus, specifically for perforation of well tubing to drain fluid.
2. Description of Prior Art
The present invention relates to methods and apparatus for perforating tubing inside a subsurface well, and more specifically to manually-dropped perforating assemblies for use in perforating tubing inside a well.
The present inventor was granted U.S. Pat. No. 5,148,868 Christian (1992), for a manually-dropped perforating assembly that uses an explosive charge within a percussion firing assembly. U.S. Pat. No. 5,148,868 is machined from cylindrical lengths of metal pipe and includes a firing pin disposed within said perforating assembly. When firing pin is in an armed position and subjected to sharp force it strikes a detonator in a shell holder. Other known perforating assemblies also use explosive charges.
In today's environment, use of explosive charges, however small, is not welcome in the oilfield due to liability issues and restrictions on methods of transporting explosives. For example, transporting heretofore known perforators to offshore wells by air is prohibited.
Drilling wells has been fairly standard, that is, a hole is drilled and casing is installed and tubing is placed inside the casing to convey the production to the surface. The uses of perforators in the drilling of wells and in the servicing of wells already in production are manyfold. Certain types of perforators are used to perforate holes in casing in order to start production. Such perforators are lowered to the firing point using one of three methods: lowered by an electric wireline, lowered by a slickline, or attached to the end of tubing and lowered through the casing. The latter is generally referred to as a tubing-conveyed perforator or gun. Perforators of casing are fired by an electrical firing system; by use of a drop bar, commonly referred to as a “go devil” system; or some type of hydraulic system. The expended perforator is then returned to the surface using one of the following methods: by an electric wireline, by a slickline, or pulled to the surface along with the tubing string. And, in some cases, the perforator is released into the bottom of the well and left in an area of the wellbore below the production zone called the rat hole.
Occasionally, casing perforators are used to create a borehole at a precise depth in the tubing in order to enhance production. Casing perforators are rarely used to perforate both tubing and casing.
Use of perforators for other than drilling operations is for servicing producing wells. Frequently, it is necessary to perforate the tubing, within a well casing, so that trapped fluids can drain and escape from the tubing prior to pulling the tubing string from a well. Wells with plugged tubing require the tubing string to be pulled from the well. Therefore, inventors created perforating guns designed to make drain holes in the tubing, but not the casing, through use of a controlled explosion. Explosive perforating guns, such as that disclosed in U.S. Pat. No. 4,624,307 to Kinley et al (1986), have been used to penetrate tubing.
Prior to a patent of the present inventor, U.S. Pat. No. 5,148,868, to Christian (1992), all known tubing perforators used for creating drain holes in tubing were lowered into firing position by means of a wireline; either an electric wireline or a slickline. After detonation, such perforators must be retrieved from the well before the tubing string can be pulled from the well. It is only after the tubing is pulled that the necessary steps can be taken to get the well back into production.
It is also possible to pull tubing from a well without draining the fluids from the tubing. And, pulling tubing without a drain hole is less costly than using a perforator which must be lowered by wireline. Several problems can occur when tubing is pulled without a drain hole. The time required to pull tubing from a hole is increased due to the problem of trying to contain the fluids trapped in the tubing. A bucket designed to wrap around the connections of the tubing can be used. A hose is attached to the bottom of the bucket at one end with the other end attached to a tank which is mounted on a truck. When a tubing string section is unscrewed from another section, the fluids trapped inside flow into the tank. Some of the fluids invariably spill onto the surface. Clean up of such spillage is mandated by state regulation, and when contamination occurs outside the location of the well, clean up is mandated by the Environmental Protection Agency.
The following is a description and the disadvantages of these various known methods of perforating tubing:
U.S. Pat. No. 5,148,868 to Christian, Sep. 22, 1992, discloses a method and apparatus for perforation of well tubing that incorporates a mechanically detonated firing head. An explosive charge is required to create a drain hole through well tubing, so U.S. Pat. No. 5,148,868 creates a drain hole with the use of explosives. The apparatus described can be dropped by hand, eliminating use of electric wireline or slickline operations to lower and to retrieve the apparatus. The method used to lower and to retrieve the present invention is the same as U.S. Pat. No. 5,148,868. The difference is an explosive charge, which could prematurely detonate, required to use U.S. Pat. No. 5,148,868, is not required to use the present invention. And, another difference is the design of the apparatus disclosed is more complex than the present invention.
U.S. Pat. No. 4,911,251 to George, et al., Mar. 27, 1990, discloses a method and apparatus for actuating a tubing-conveyed perforating gun, utilizing a firing head and two pistons, one releasable through mechanical force and the other through hydraulic force. The method disclosed requires initiating a burn or an explosion to detonate a perforating gun lowered into well tubing using a wireline or slickline. George et al. does not allow use of a perforating apparatus without a burn or explosives which are safety issues. George et al. does not allow use of a perforating gun without the time-consuming and malfunction-prone use of a wireline or slickline.
U.S. Pat. No. 4,624,307 to Kinley et al., Nov. 25, 1986, discloses an explosive perforating tool conveyed by wireline or slickline and consisting of numerous parts. Kinley does not allow creating drain holes without the use of dangerous explosives, and its complex design is prone to malfunctioning. The method described in U.S. Pat. No. 4,624,307 to lower and raise the perforating tool requires the time-consuming use of an electric wireline or slickline; methods prone to malfunctioning.
U.S. Pat. No. 4,632,034 to Colle, Jr., Dec. 30, 1986, discloses redundant detonation initiators for use in wells; and methods and apparatus for detonating high explosive devices downhole in a well. Colle, Jr. does not allow creation of drain holes without the use of dangerous explosives.
U.S. Pat. No. 4,566,544 to Bagley, et al., Jan. 28, 1986, discloses a drop bar firing system for a tubing-conveyed armed perforating gun; a drop bar that contacts a firing head. Bagley does not allow creation of drain holes in tubing without use of dangerous explosives.
Unlike prior art, the present invention, a non-explosive perforating apparatus, is safe to use because no detonator and no shell is required. There are several reasons the present invention is less costly to manufacture, use, and redress than heretofore known wireline and slickline perforators.                The present invention does not require a license from the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to store, transport and use because no explosive charge is required. Adherence to special handling and special storage regulations mandated by ATF is not required.        The present invention can be shipped abroad which is not possible with heretofore known perforators due to U.S. Department of Homeland Security restrictions.        The present invention is a simple design, so its manufacture, use, and redressing is less complex than heretofore known perforators.        The present invention does not require multiple moving parts, so the possibility of a malfunction delaying a successful perforation is extremely low.        The present invention can be manually dropped into well tubing from the surface, so its use does not require a wireline truck, and two workers a wireline operator and a helper.        The present invention permits the removal of tubing string with no time-consuming separate step required to retrieve it.        
3. Disadvantages of Prior Art
Thus, heretofore known methods and devices for perforating tubing suffer from a number of disadvantages as set forth below along with reasons the present invention is superior. The following details these disadvantages and provides the reasons this non-explosive, manually-dropped perforator with two methods of activation, hydraulically-activated or fluid-activated, is totally safe and much less costly to use:
(a) Workers can be injured when handling and using a wireline or slickline perforator because required explosive charge can detonate prematurely. This invention does not require an explosive charge, so is safe to use.
(b) With the use of heretofore known perforators of complex design, more frequent malfunctions result because a large number of parts are required which leads to time-consuming repairs, more costly manufacture, and wireline operator training. The present invention is not a complex design so requires minimal repairs, lower manufacturing and redressing costs; and no special worker training costs.
(c) With the use of an electrically-detonated wireline perforator, workers can be injured when premature firing occurs due to electrical interference, such as radio waves. The present invention is hydraulically- or fluid-activated, so premature activation cannot occur.
(d) A second perforator may need to be lowered when a firing head on a wireline-conveyed perforator malfunctions, a problem which occurs because the firing heads are comprised of several moving parts. This is not a problem with the present invention because it has no firing head and is designed to be activated with two moving parts when using a drive-wedge method of activation, and with one moving part when an alternative fluid-method of activation is used, not requiring a wedge.
(e) Wireline perforators cannot be retrieved from a well along with the well tubing string. The present invention is designed so that extra steps are not required to retrieve the apparatus.
Prior art does not provide an apparatus that can be activated without an explosive charge and does not provide a system of such noncomplex, trouble-free design.